Massive multiple-input multiple-output (MIMO) provides an effective means for significantly increasing the capacity of cellular communication systems while possibly reducing their energy consumption. Multiple-Input-Multiple-Output (MIMO) antenna techniques are key factors in achieving the high data rates promised by next-generation wireless technologies such as LTE (Long-Term Evolution), LTE-Advanced and planned 5th generation technologies.
MIMO systems are designed to take advantage of spatial diversity available in the propagation environment. The spatial diversity is quantified by the correlation between antennas, a function of both the propagation environment and the antenna patterns. Under ideal conditions an M×N MIMO system (one using M transmitting antenna elements and N receiving antenna elements) can increase maximum data rates by a factor of min{M,N} times those available from a Single-Input Single-Output (SISO) system operating in the same bandwidth. In other words, a 4×2 MIMO system can (under ideal conditions) double the data rates available in a SISO implementation, while a 4×4 MIMO system can potentially quadruple those rates. However, classical array modeling via MIMO emulation is expensive and prohibitively complex to build, and channel emulators have a limited number of possible inputs.
As the demand for higher bandwidths continues to grow, designers use higher frequencies—for example, as high as 60 gigahertz. When higher frequencies are used, the size of transmit antenna elements decreases, with a result that each element produces lower path gains—with a resulting power change of as much as 30 dB less. The use of massive MIMO boosts resulting beam signal strength. There is also a demand for multiple users in the same cell with separate signals, called multiple-user MIMO.
Emulation of massive MIMOs makes it possible to group hundreds of fading links computed in hardware into a tractable number of virtual elements, for increasing data rates and for testing for massive MIMOs.
An opportunity arises to provide systems and methods for testing massive MIMO arrays.